For example, the technique disclosed in Japanese Patent Application Laid-Open (JP-A) No. H03-84286 is an example of a floor structure that is made of metal and that, although ensuring strength and rigidity of the floor portion of a vehicle, is easy to mold. To describe this structure briefly, the floor portion is formed by being divided into a floor plate that has a flat shape and a tunnel member whose cross-sectional shape is formed in a substantially U-shape, and the tunnel member is fixed to the top surface of the floor plate. At this time, the front end portion of the tunnel member is joined to a front wall (dash panel) that is provided erect at the front end portion of the floor plate, and the rear end portion of the tunnel member is joined to a rear wall (back panel) that is provided erect at the rear end portion of the floor plate. On the other hand, in recent years, techniques of forming a floor portion of fiber-reinforced plastic have been proposed (e.g., JP-A No. 2008-155700).